1. Field of the Invention
This invention relates to a special effect processing device for performing special-effect processing on a 1-bit digital signal obtained by .SIGMA..DELTA. modulation.
2. Description of the Related Art
A .SIGMA..DELTA. modulated fast 1-bit signal is of the form of an extremely high sampling frequency and a short data word length, such as a sampling frequency equal to 64 times 44.1 kHz and a data word length of 1 bit, thus exhibiting a broad transmission frequency range as compared to a so-called multi-bit digital signal with a sampling frequency equal to 44.1 kHz and a data word length of 16 bits so far used in conventional digital audio. The audio range of 20 kHz is sufficiently lower than the over sampling frequency equal to 64 times 44.1 kHz thus assuring a high dynamic range. This feature can be exploited for application in a high sound quality recorder or for data transmission.
A circuitry employing .SIGMA..DELTA. modulation itself is not new and is frequently used in an A/D converter because the circuit structure lends itself to IC implementation and enables an analog to digital converter to be produced relatively easily. A .SIGMA..DELTA. modulated signal can be passed through an analog low-pass filter having a simpler structure for conversion to an analog audio signal.
On the other hand, it has been difficult to directly apply a special effect processing, such as distortion processing, indispensable for a digital audio editor, to the fast 1-bit audio signal. Thus there is no alternative but to apply special effect processing to the analog signal and to convert the analog signal processed by .SIGMA..DELTA. modulation into a fast 1-bit audio signal.
Meanwhile, for producing the fast 1-bit audio signal, processed with special effect processing by the method described above, an analog effector device is required for applying a special effect processing on the analog audio signal. On the other hand, if an audio signal in a 1-bit form is processed with special effect processing, it needs to be reverted to an analog audio signal to which a special effect processing and .SIGMA..DELTA. modulation needs to be applied, thus complicating the circuit structure. In addition, the 1-bit signal is transiently converted into an analog audio signal, thus lowering the signal quality of the 1-bit audio signal.